Ears and Kidneys: What's the Connection
(Source: Boystown Research Registry)

There are a number of genetic and non-genetic disorders that affect both ears and kidneys. However, the types of problems may be different, and the reasons that both ears and kidneys are involved may be due to different processes in development. The kidney problems can include malformed or missing kidneys or problems at a microscopic level; the ear problems may include malformation of the external ear or the ossicles (small bones) of the middle ear, or microscopic changes in the cochlea. These point up several areas of similarity between the ears and kidneys. These are similarities in structure, function, or in the timing of prenatal development, that is, the period of development of the baby during pregnancy.

When seen through the microscope, the kidney and the cochlea of the inner ear have some very similar membranes which are held together with a substance called collagen. These membranes are similar in function and in structure (the way they are put together). In both cases, these membranes help maintain the chemical balance of the fluids of the kidney and inner ear. Because of similar molecular structure, they can be damaged by the same drugs, such as overdose of diuretics.

In the developing baby, both the ear and kidney develop around the 5th to 8th week of pregnancy. Thus, a genetic problem in coordinating development at that time, or a non-genetic problem, such as an infection, might affect the development of both areas at the same time. Several examples can be given to show how different problems can influence both the ears and the kidneys in different ways. The Branchio-oto-renal syndrome (BOR) involves the external and middle ear structures along with the kidneys. Some people have also been found to have a duplication of the ureters, which are the tubes leading from the kidney to the bladder. Since this has been found to be more common in some families than in others, one researcher has suggested that it might be a separate syndrome and named it the BOU syndrome for Branchio-oto-ureteral--or even BOUU, to remind one of the duplication! These conditions are quite variable, and a person with the gene may have only one of the minor characteristics, or they may have serious hearing and kidney problems. In both of these syndromes, the ear and kidney problems appear to be primarily problems of prenatal development. One researcher, Dr. Michael Melnick, has suggested the reason ears and kidneys are both affected is because they develop at the same time. For example, there may be something which affects cell division at that particular point in prenatal development.

Other syndromes affect the ear and the kidney more at the biochemical level. Alport syndrome includes hematuria (blood in the urine) and nephritis (kidney disease), along with progressive hearing loss. Presumably, the cause of these functional problems involves the molecular similarities between the cochlea and the kidney. For some reason, both membranes tend to deteriorate over time, leading to progressively worse kidney problems and worsening hearing. Interestingly, correction of the kidney problems by transplantation sometimes halts the progression of the hearing loss, which suggests that additional factors in the blood, such as the toxicity that goes along with kidney failure, may further damage the hearing. Thus, in these syndromes, there is not a problem with formation of the kidney or cochlea, but in their continued function.

Examples of other syndromes with hearing loss and renal problems include:

Charcot-Marie-Tooth disease and deafness. This is an autosomal dominant condition. Charcot-Marie-Tooth disease is a progressive nerve disease which causes gradual decrease of muscle function in the legs. The hearing loss is sensorineural and usually is noted in adolescence and gets progressively worse. Some people also have nephritis, or kidney disease, with this condition.

Epstein syndrome (Macrothrombocytopathia, nephritis, and deafness). This is an autosomal dominant syndrome that is very much like Alport syndrome, except that it also includes a defect of the platelets, the cells of the blood that aid clotting. There is also a very similar condition, called the Fechtner syndrome, that has abnormalities of the white blood cells as well.

Muckle-Wells syndrome (urticaria, deafness, and amyloidosis). This is an autosomal dominant condition with recurrent fever, skin rash (urticaria), joint pain, progressive sensorineural hearing loss, and amyloidosis of the kidneys, which is an accumulation of a protein in the kidney which gradually blocks its function. The hearing loss usually begins in childhood, while the other problems may not be seen until adolescence.

Renal tubular acidosis and hearing loss. This is an autosomal recessive condition involving sensorineural hearing loss and formation of kidney stones. There appear to be two types. In one, the hearing loss is profound and present at birth, and the kidney problems, which occur very early in infancy, can be severe if not treated. In the other type, the kidney stones and hearing loss do not appear until adolescence. The kidney problems are milder, and the hearing loss is progressive.

Townes-Brock syndrome. This autosomal dominant condition can be quite variable within families. The characteristics include lack of an opening for the anus which must be repaired at birth, abnormal bones of the hands or feet, kidney problems (usually small, poorly formed kidneys), "lop" shaped ears, and mild sensorineural hearing loss.

Oto-renal-genital syndrome. This is a rare recessive condition involving abnormal middle ear ossicles, incomplete formation of the kidneys, and abnormalities of the reproductive organs. Genetic research into syndromes with both renal and auditory problems will be very valuable in telling us how the damage is done to these two systems and hopefully will provide means of therapy, particularly for life-threatening renal disease.

Date Originally Created: Winter of 1989.
The information presented here first appeared in publications of the Boys Town National Research Register for Hereditary Hearing Loss, the National Institute on Deafness and Other Communication Disorders (NIDCD), Hereditary Hearing Impairment Resource Registry (HHIRR), or the Boys Town Research Registry for Hereditary Hearing Loss.

The Boys Town Research Registry for Hereditary Hearing Loss

The Boys Town Research Registry for Hereditary Hearing Loss (Registry) is designed to foster a partnership between families, clinicians and researchers in the area of hereditary hearing loss/deafness through three primary functions. First, the Registry disseminates information to professionals and families about clinical and research issues related to hereditary deafness/hearing loss. Second, the Registry collects information from individuals interested in supporting and participating in research projects. This information is used to support the third function of the Registry - matching families with collaborating research projects.